1. Field of the Invention
The present invention relates to a method of manufacturing a bead filler and an apparatus for forming a filler portion, and more particularly to a method of manufacturing a bead filler constituted by a core portion and a filler portion and disposed in a curved side portion of a pneumatic tire and a filler portion forming apparatus for forming the filler portion.
2. Description of the Related Art
In a turned-up portion of a carcass ply disposed in the side portion of a pneumatic tire, a bead filler composed of a bead core and a filler portion is disposed. The bead core of the bead filler is formed in a circular ring shape by twisting a plurality of cords into one. On the other hand, the filler portion is made from a rubber composition having a predetermined length, and is formed by linearly extruding the rubber composition in a substantially triangular cross sectional shape having a thick base portion and a thin top poriton. The filler portion having a substantially triangular cross sectional shape is disposed in such a manner that one side of the triangle is brought into contact with the carcass ply main body portion 12A, one side is brought into contact with a bead core 22 and one side is brought into contact with a carcass ply turned-up portion 12B, as shown in FIG. 2.
In a process of manufacturing a tire, as shown in FIG. 7, a filler portion 82 extruded to a predetermined length is wound around a periphery of a bead core 84 having a circular ring shape. At this time, since the filler portion 82 is in a linearly extruded belt shape, it is wound substantially in a perpendicular state along an axial direction of the ring-like bead core 84 such that a top portion of the filler portion 82 is disposed in a perpendicular state to a radical direction of the bead core 84. When the winding start end is first mounted to the bead core 84 and the filler portion 82 is wound around once in a manner that a base portion of the filler portion 82 is disposed to contact with a peripheral portion of the bead core 84, the winding finish end overlaps and presses onto the winding start end. Accordingly, the winding start end and the winding finish end are joined, and a bead filler 80 integrally constructed by the filler portion 82 and the bead core 84 is formed.
As shown in FIGS. 7A and 7B, in the constructed bead filler 80, in which the filler portion 82 is disposed along an axial direction of the bead core 84, the filler portion 82 is pulled by the top portion thereof in the direction shown by the arrow M and is formed in a shape similar to the shape of the side portion of the pneumatic tire. Next, the bead filler 80, formed in the shape similar to the shape of the side portion of the pneumatic tire, is mounted on the carcass ply placed on a forming drum and disposed in the side portion of the pneumatic tire by turning up the turned-up portion 12B of the carcass ply around the bead filler 80.
In this case, when the top portion of the filler portion 82 is pulled to resemble the shape of the side portion of the pneumatic tire, the rubber composition is stretched out at the top portion of the filler portion 82 so that the diametrical size is greatly increased. At this time, since the base portion of the filler portion 82 is joined to the bead core 84, the diametrical size of the base portion of the filler portion 82 is only slightly changed. Accordingly, a large difference in diameter is generated between the base portion and the top portion of the filler portion 82.
Due to this difference in diameter, the amount of the opening is anticipated in advance and the rubber composition is excessively overlapped at that portion so that the joined portion does not open up at the top portion of the filler portion 82. Accordingly, even if the joined portion is stretched when the diametrical size has increased greatly by pulling up the filler portion 82, the winding start end and the winding finish end of the filler portion 82 are not separated from each other, so that a bead filler 80 formed in a shape similar to the shape of the side portion of the pneumatic tire can be obtained.
However, when the anticipated amount of opening is great, the overlapped amount becomes great. Accordingly, there are cases where a great difference in thickness is generated between the overlapped portion and the portion not overlapped. Further, the front end of the bead filler 80 is stretched by the anticipated amount so as to be the original thickness, however, the base portion which is overlapped by the same amount as the top portion is less stretched than the top portion. Accordingly, there are cases where the thickness of the filler portion 82 is uneven in the overlapped portion. As mentioned above, when unevenness is generated in the filler portion 82 along the circumferential direction of the side portion of the pneumatic tire, the unevenness becomes an unevenness along the circumferential direction of the side portion of the pneumatic tire, so that the uniformity of the pneumatic tire is deteriorated.